Magnetic Resonance Imaging (MRI) is a popular tool for performing clinical diagnoses because it is non-invasive and because it can provide information on the anatomy, function, and metabolism of tissues in vivo. The MRI technique uses powerful magnets to align the nuclear magnetic moment of hydrogen atoms (protons) found in water inside the tissue of a human body. The magnetic field aligns the protons along the direction of the magnetic field produced by the MRI scanner. The MRI scanner then emits radio frequency waves to disrupt the alignment of the protons. The protons found in different tissues in the body respond differently to the disruption, and realignment times vary accordingly. The realignment times are referred to as relaxation times T1 and T2. During realignment, the protons will emit their own radio frequency wave. The exact frequency and intensity depends on the relaxation times, and the emitted radio frequencies are sensed by detectors to form the MRI image.
The intrinsic contrast provided by the T1 and T2 relaxation times is often too limited to enable a sensitive and specific diagnosis. For that reason, MRI Contrast Agents are used to reduce the relaxation times, which sharpen the image contrast. Contrast agents are predominantly used to shorten the T1 relaxation time, although T2 contrast agents also exist. The T1 contrast agents usually contain a paramagnetic metal ion, which has been chelated so as to avoid toxicity within the body.
Such chelated paramagnetic metal ions commonly include the gadolinium ion (Gd+3). Some commercially available T1 contrast agents of this type include: Gd-DTPA (gadopentetic acid), Gd-DOTA (gadoteric acid), Gd-DTPA-BMA (gadodiamide), and Gd-DO3A (gadoteridol). However, paramagnetic contrast agents only provide a modest decrease in T1 relaxation time. Additionally, the paramagnetic contrast agents only respond weakly to the magnetic field produced by the MRI scanner. Therefore, the signal-to-noise ratio between some tissues, especially between pathological tissue and its surrounding healthy tissue, remains low, making diagnosis based on the produced images difficult. Further, because the paramagnetic contrast agents only respond weakly to the magnetic field of the MRI scanner, the MRI scanner must operate at very high magnetic field levels.
Disclosed herein are embodiments of a ferromagnetic nanoparticle that has great applicability, among other applications, as T1 and T2 MRI Contrast Agents. These particles have a magnetic moment that is greater than ten times that of paramagnetic contrast agents. Also disclosed herein are exemplary methods for producing the particles. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.